1. Field of the Invention
This invention relates generally to techniques for performing wellsite operations. More specifically, the invention relates to techniques for controlling (e.g., circulating) fluid flow-through a drill string.
2. Description of Related Art
Oilfield operations are typically performed to locate and gather valuable downhole fluids. Oil rigs are positioned at wellsites and downhole tools, such as drilling tools, are deployed into the ground on drill strings to reach subsurface reservoirs. During drilling, mud may be pumped into the drill string from a top drive in order to lubricate and/or rotate a drill bit, and control pressure in the drill string. The drill string may be formed of several drill string segments (or pipe segments, drill pipe, pipe joints, casing, landing strings, cross-over subs or other tubulars) coupled together on a rig at the surface. During the connection of the pipe segments, the top drive may be disconnected from the drill string, thereby stopping the flow of drilling mud into the drill string. Once the downhole tools form a wellbore to reach a desired reservoir, casings may be cemented into place within the wellbore, and the wellbore completed to initiate production of fluids from the reservoir. Tubing or pipes are typically positioned in the wellbore to enable the passage of subsurface fluids to the surface.
During drilling, it may be desirable to control fluid pressure of the drill string. For example, the fluid pressure of the drill string may be controlled with fluid flow from a top drive during drilling. In another example, the fluid pressure in an annulus surrounding the drill string may be controlled (e.g., circulated) during the connection operation. Some examples of drilling mud pressure control techniques are provided in U.S. Pat. No. 7,726,418, 2009/0205838, International Patent Application No. WO2009/067588 (US20100270034) and WO2009/067485 (US20100252276). However, in some cases, fluid pressure may not be controlled during drilling operations. For example, the drilling mud may be pumped into the drill string during drilling, but may be left uncontrolled during the connection of the pipe segments.
Despite the development of techniques involving drilling mud pressure control, there remains a need to provide advanced techniques for controlling pressure during drilling operations. The invention is directed to fulfilling these needs in the art.